A book as redundant as the sick and degenerate nature it describes. In the distant future outlined by Aldiss, the radiation produced by the Sun turning nova and the general collapse of the solar system lead to the near extinction of mammals and the proliferation of monstrous and malignant plant life. Humans have returned to the trees and devolved, not turning back into apes but something akin to aphids, and their intelligence has been greatly diminished.
In all this, the adventures of a few of these humans, some in search of a new place in the world, some, subjugated by a fungus, sentient but not particularly intelligent, are driven to adventures bordering on self-harm. The final reunion between the protagonists gives more of a feeling of "let's end it here, I don't know what to come up with anymore" than a real thoughtful conclusion to the story.